This invention relates generally to processes and equipment for the removal of water from coal fines and other organic particulates and more specifically to the drying of coal fines using a polarized gas stream deployed in a continuous flow system.
Younger coal, such as sub-bituminous coal found in the Western United States and elsewhere, can have excessive amounts of moisture, defined generally as water content greater than fourteen percent (14%) by weight. This moisture is difficult to remove because it is "inherent" in the coal (i.e., retained in the molecular structure of the coal). Many surface coals gradually lose their moisture over a period of time and reach an equilibrium of about eight percent (8%) moisture content, which is well suited for commercial use.
Moisture content detracts from and reduces the BTU (British Thermal Unit) value of the coal. The moisture content of sub-bituminous coals has been a historical barrier to commercial exploitation of these coals. The water found in these coals has been shown to be as high as thirty-three percent (33%), virtually reducing the recoverable BTU's to half the expected levels for normal coal product. The following Table 1 illustrates the relationship.
TABLE NO. 1 ______________________________________ Moisture Content Net BTU ______________________________________ 8% 14,000 plus 12% 12,000 30% 7,400 33-34% 6,700 ______________________________________
The adverse impact of moisture is not limited to the net combustion efficiency or other production related effects. When the water content reaches the levels that are found naturally in some coals, the economics of shipping the water itself becomes a drawback to the utilization of the coal product.
The presence of excess moisture in an otherwise usable coal product renders it commercially useless at worst and makes it barely marketable at low pricing at best. Similar problems exist with other organic products that contain excess moisture.
In the past, where it was determined to be economically feasible, attempts have been made to reduce the water content of coal with excess inherent moisture. Previous methods typically employed waste heat as the direct method for vaporizing the water held within the particle matrix. If waste or inexpensive heat was not available, it was generally found to be uneconomical to dry coal fines in this manner.
Other methods have been employed to reduce the moisture content of coal fines without resorting to heat. These have focused primarily on the ability of water to form partial solutions with low boiling organics such as the low molecular weight alcohols. Under these processes, the combined alcohol and water mix is allowed to be vaporized under ambient or low heat conditions. The recovery of the organic material is typically necessary to maintain economic practicability.
Another process utilizing a naphtha stream is known to be useful in removing water from adsorbents. In this process, the naphtha stream is a reluctant water vehicle and under quiescent conditioning, the water is separated from the vehicle. The process takes place under conditions of elevated temperature.
An object of the present invention is to provide an improved method and apparatus for removing moisture from coal that is efficient and does not require expensive heat or chemical reagents.